In liquid chromatography, degassers are used to reduce the amount of gas dissolved in the solvents used. The solvents used in liquid chromatography are typically stored in contact with the surrounding air so that they are usually in a gas-saturated state. These dissolved gases adversely affect the chromatographic measurements.
If a solvent mixture is used, for example alcohol/water, the gas solubility of the mixture may be less than that of the liquids it contains. This leads to the formation of gas bubbles which have detrimental effects on the stability of the system flow and the composition of the solvents. This effect plays a particularly important role in low-pressure mixing systems.
Oxygen dissolved in a solvent adversely affects detection sensitivity. In UV detection, the high solubility of oxygen in eluents is noticeable, and large fluctuations of the oxygen concentration can lead to pronounced detection noise at wavelengths below 260 nm. The high absorbance can even be used to measure the oxygen content.
In fluorescence the presence of oxygen causes the quenching effect which may lead to a suppression of the fluorescence detection. For this reason, sensitive measurements with a fluorescence detector can only be made when using degassed solvents.
In addition to the influence of dissolved gases on detection, chemical reactions of dissolved gases with the eluents also present a problem. This may adversely affect the analysis results, especially in biological analyses.
Because of the aforementioned adverse effects of dissolved gases on analysis results, it is imperative to degas the liquids being used. Several methods for degassing are known in the art, for example, heating, boiling, ultrasonic degassing, helium degassing, vacuum degassing. U.S. Pat. No. 4,469,495 describes a liquid chromatography degasser for removing oxygen or other dissolved gases from liquid, wherein the liquid being degassed is passed through a spiral-shaped tube. This tube is made of a synthetic resin material, such as polytetrafluoroethylene. U.S. Pat. No. 4,729,773 describes a device for degassing liquids in which the liquid is passed through a tube made of a fluor-resin which allows gases to pass through it while preventing the liquid from doing so. Degassers using flat membranes are known from U.S. Pat. No. 3,751,879 and from U.S. Pat. No. 3,735,562. Known degassers are often complicated to manufacture and to handle and thus costly, and may have variations in degassing efficiency when the type of solvent to be degassed changes. Another degasser using a flat membrane is known from EP 718016.